The question What would you say vs. How would you say has been marked as a duplicate of How do you call..? vs. What do you call…?. They can only be duplicates if say and call are grammatically and semantically equivalent in the two questions.
But this is not the case. Call is being used as a transitive verb in a request to name a noun (phrase). For example: How/What do you call a person who eats fish but no meat? Answer: A pescatarian.
Say is followed in the other question by a temporal clause. not an object. Its clear purpose is to elicit a complete sentence answer from an English learner in what is called a display question.
The OP of What would you say vs. How would you say states I want to ask a question what someone would say in or about a certain situation. I don't think she will find a useful answer in the duplicate.